Influence of the surface stress on the size-dependent elastic behavior of silicon nanowires

A recent study has highlighted an existing controversy among experimental measurements and theoretical models on the size-dependent elastic behavior of silicon nanowires. Some measurements have depicted a significant size-dependent elastic response, while several studies report a negligible change on the elastic modulus of silicon nanowires through size reduction. To address such contrast, this work studies the surface stress contribution on the size-dependent elastic behavior of silicon nanowires. Molecular dynamics simulations are employed to investigate the influence of size, crystal orientation, boundary condition, and the residual surface stress on the incorporation of the surface stress in the mechanical properties of silicon nanowires. This is accomplished by a primary atomic stress analysis. The implication of the surface stress on the bending behavior is then calculated for silicon nanowires along 100 and 110 crystal orientations having { 100 } and { 100 } / { 110 } transverse surfaces, respectively. This study demonstrates, for the first time, the role played by the surface stress to reduce the elastic modulus of 110 silicon nanowires, which is comparable with experimental measurements on wires with the same size and crystal orientation. The present work enlightens the incorporation of the surface stress on the mechanical behavior of silicon nanowires for the explanation of existing studies and implementation for future investigations.